Signal Transducer and Activator of Transcription (STAT) proteins are a family of transcriptional activators essential for many growth factor signaled responses. Stat4 is specifically activated by a small set of cytokines, including interleukin (IL)-12 and IL-23, and has been implicated in biological responses including inflammation and the development of T helper (Th) type 1 effector cells. It is not well understood how Stat4 regulates gene expression and immune function. Using Stat4-deficient and Stat4-transgenic mice as a model, this proposal will investigate the mechanisms by which Stat4 functions. In the previous grant period, we have demonstrated distinct gene profiles activated by the Stat4 isoforms Stat4a and Stat4B. We have further begun to understand how Stat4 mediates gene induction by examining chromatin remodeling following IL-12 stimulation. In this grant renewal application, we propose to examine the ability of Stat4 isoforms to mediate inflammation in vivo using a model of granuloma formation and in a model of experimental autoimmune encephalomyelitis. We will continue our analysis of Stat4-mediated chromatin remodeling using the IL-18Ralpha gene as a model for genes that can be transiently induced by IL-12 and require Stat4 for expression in Th1 cells to understand how Stat4 mediates differentiation specific gene expression. Finally, we will examine the requirement for Stat4 in the generation of IL- 23 biological responses. IL-23 is a recently described cytokine that activates Stat4. However, the requirement for Stat4 in mediating the pro-inflammatory activity of IL-23 has not been explored. The overall goal of this renewal application is to focus on defining the role of Stat4 in cytokine responses and transcriptional regulation during inflammatory processes. Our hypothesis is that Stat4 mediates inflammatory disease by coordinating signals from multiple cytokines to confer long lasting changes in gene expression. Our experiments will allow a greater understanding of inflammatory signaling and resulting gene regulation. These studies will characterize known, and identify new, biological targets for pharmaceutical treatment of chronic inflammation and autoimmunity.